Abstract: High pressure heat treatments at temperatures of 920-980 ℃ and pressures of 1-6 GPa were conducted on TC9 titanium alloy. The microstructure, hardness, compressive strength and plastic deformation resistance of the alloy after high pressure heat treatments were studied and were compared with those after normal pressure annealing at 950 ℃. The results show that the α phase in the microstructure of the TC9 titanium alloy was significantly refined after high pressure heat treatment compared with that after normal pressure annealing at 950 ℃, and was the smallest in size at temperature of 950 ℃ and pressure of 3 GPa. After heat treatment at 950 ℃ and a pressure of 3 GPa, the small blocky α phase and fine needle-shaped α' martensite were formed in the titanium alloy. Moreover, the hardness and the compressive strength at room tempearature and at 500 ℃ of the alloy increased by 12.95%, 7.33% and 8.89% those after normal pressure annealing at 950 ℃, respectively, and the plastic deformation resistance was improved.